Some computing devices receive user input and process the user input in order to provide text auto-completion, spelling correction, and grammar correction functionality. Such computing devices can also provide the user input as training data for text processing services that provide the functionality. A user may specify the user input with a virtual keyboard or using a speech recognition system. Textual content specified by the user input may be placed into a document during document composition, or into a field of a web form. The textual content may include non-prose text (e.g., credential data that includes a seemingly random collection of alphanumeric characters). The non-prose text may not be very helpful as training data for such text processing services. Further, the non-prose text may include information that the user may not want to share with such text processing services.